Some sewing machines include a lower looper and an upper looper. The lower looper moves back and forth interlockingly with a vertical motion of a needle so as to be inserted into a loop of a needle thread formed below a throat plate. The upper looper is projectable above from the throat plate to insert an upper looper thread into a loop of a lower looper thread inserted in the loop of the needle thread by the lower looper. According to one technique, the sewing machine may be configured such that a use and a nonuse of the upper looper is selectable, so that a sewing work can be switched between a mode in which a sewing is carried out by a cooperation of the needle, the lower looper and the upper looper and another mode in which a sewing is carried out only by the needle and the lower looper without using the upper thread (see, e.g., JP 7-39668 A). This sewing machine includes a retracting mechanism operable to retract the upper looper to a lower position when the nonuse of the upper thread is selected. According to another technique, the sewing machine may include a threading mechanism which ejects compressed air toward thread holes at respective tip portions of the lower looper and the upper looper to insert the threads into the thread holes (see, e.g., Japanese Patent No. 2865470).
While the needle thread is caught by the lower looper or while the lower looper thread is caught the upper looper, threading the threads through the thread holes of the respective loopers is complicated, because the thread caught by the looper needs to be pulled and the order of inserting the threads needs to be considered. Further, if the threads are inserted through the thread holes of the loopers while the threads are caught by the respective loopers, the threads may not entangle with each other so that a seam may not be formed in a subsequent sewing work. Therefore, at the time of inserting the threads through the thread holes of the upper looper and the lower looper, it is preferable that the threads are not entangled with each other, namely, it is preferable that the needle is at its upper position, the lower looper is at its rear position and the upper looper is at its lower position. In other words, it is desirable that the threading mechanism is operable to retract the upper looper to the lower position while carrying out the threading.
It is desirable that both the retracting mechanism operable to retract the upper looper to the lower position when the upper looper is in nonuse and the threading mechanism operable to insert the thread (the upper looper thread) through the upper looper are incorporated into the sewing machine. However, if both of the mechanisms are incorporated into the sewing machine by combining the techniques disclosed in JP 7-39668 A and Japanese Patent No. 2865470, it is necessary to provide means for moving the upper looper to the lower position (i.e., the retracting position) for each of the mechanisms. Thus, a configuration becomes is very complicated and the number of components increases.
Moreover, according to the sewing machine disclosed in JP 7-39668 A, a switching operating portion for switching the use and nonuse of the upper looper is disposed on an inner side of a sewing machine cover. Therefore, the sewing machine cover needs to be opened in order to operating the switching operating portion. In addition, operability is poor because a working space is restricted inside the sewing machine cover.